-Analysis and discussion on the powder drop during the production of lithium-ion batteries

Analysis and discussion on the powder drop during the production of lithium-ion batteries
author:enerbyte source:本站 click379 Release date: 2023-01-31 09:24:29
abstract:
The current production process of lithium cobalt oxide flake powder dropping basically does not drop powder. The factors affecting the possibility of powder dropping in the production process include:1. The formula proportion is improper, such as too little adhesive and too little volume agent, resu...

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The current production process of lithium cobalt oxide flake powder dropping basically does not drop powder. The factors affecting the possibility of powder dropping in the production process include:

1. The formula proportion is improper, such as too little adhesive and too little volume agent, resulting in uneven mixing.

2. The baking temperature of the adhesive is too high, which will damage the structure of the adhesive,.

3. The slurry mixing time is not enough, and it is not fully mixed,

4. The temperature is too low during coating, and the electrode is not dried.

5. The coating amount is uneven and the thickness difference is too large.

6. The pole piece is not baked before rolling and absorbs a large amount of water in the air.

7. The pressure is too high during rolling, which causes the polar powder to peel off from the fluid collector.

8. When rolling, the pole piece is not delivered in the right way, resulting in uneven stress on the pole piece.

9. Use oil-based positive electrode, water-based negative electrode, and do not drop powder?

3、 Bad battery items and causes:

1. Low capacity

Cause:

A. The amount of attached materials is too small; B. There is a large difference in the amount of material attached on both sides of the pole piece; C. The pole piece is broken;

D. Less electrolyte e. Low conductivity of electrolyte; F. The positive and negative plates are not properly matched;

G. Low porosity of diaphragm; H. Adhesive aging → adhesive peeling off; I. The coil core is too thick (not dried or the electrolyte is not penetrated) j. It is not fully charged during volume separation; K. The specific capacity of positive and negative electrode materials is small.

2. High internal resistance

Cause:

A. False welding between negative plate and pole lug; B. False welding between positive plate and pole lug; C. False welding between positive lug and cap; D. False welding between negative lug and shell; E. The contact resistance between rivet and pressing plate is large; F. No conductive agent is added to the positive pole; G. There is no lithium salt in the electrolyte; H. The battery has been short-circuited; I. The porosity of diaphragm paper is small.

3. Low voltage

Cause:

A. Side reaction (electrolyte decomposition; impurities in positive electrode; water); B. Not well formed (SEI film is not safe); C. The customer's circuit board leakage (refers to the electrical core sent back by the customer after processing); D. The customer did not spot weld as required (the electric core processed by the customer);

E. Burrs; F. Micro short circuit; G. Dendrites are produced at the negative electrode.

4. The causes of over-thickness are as follows:

A. Weld leakage; B. Electrolyte decomposition; C. Undry moisture; D. Poor sealing of cap; E. The shell wall is too thick; F. The shell is too thick; G. The coil core is too thick (too much attached material; the pole piece is not compacted; the diaphragm is too thick).

5. The causes are as follows

A. Not well formed (SEI film is incomplete and dense); B. The baking temperature is too high → the adhesive is aged → the material is removed; C. Low specific capacity of negative electrode; D. The positive electrode has more materials and the negative electrode has less materials; E. Cap leakage and weld leakage; F. Electrolyte decomposes and conductivity decreases.

6. Explosion

A. The divider is faulty (causing overcharge); B. Poor diaphragm closing effect; C. Internal short circuit

7. Short circuit

A. Material dust; B. The shell is broken when it is installed; C. Ruler scraping (small diaphragm paper is too small or not well padded); D. Uneven winding; E. Not packed properly; F. Diaphragm has holes; G. Burr

8. Open circuit

a) The pole lug and rivet are not welded well, or the effective welding spot area is small;

b) The connecting piece is broken (the connecting piece is too short or too low when welding with the pole piece)

4、 Safety characteristics of lithium ion batteries

Lithium ion battery has been widely used in people's daily life, so its safety performance should definitely be the first assessment index of lithium ion battery. As for the assessment indicators of the safety performance of lithium-ion batteries, very strict standards have been set internationally. A qualified lithium-ion battery should meet the following conditions in terms of safety performance.

1) Short circuit: no fire or explosion;

2) Overcharge: no fire or explosion;

3) Hot box test: no fire and explosion (150 ℃ constant temperature for 10min)

4) Acupuncture: no explosion (use Φ 3mm nail penetrates the battery);

5) Plate impact: no fire or explosion; (A 10kg heavy object is thrown at the battery from a height of 1m)

6) Incineration: no explosion (gas flame burns battery)

In order to ensure the safe and reliable use of lithium-ion batteries, experts have carried out very strict and thorough battery safety design to meet the battery safety assessment indicators.

1. Diaphragm 135 ℃ automatic shutdown protection: the internationally advanced Celgard2300PE-PP-PE three-layer composite membrane is adopted.

2. When the temperature of the battery reaches 120 ℃, the PE film holes on both sides of the composite film are closed, the internal resistance of the battery increases, and a large area of open circuit is formed inside the battery, and the temperature of the battery is no longer increased.

3. Composite structure of battery cover: the battery cover adopts a nicked explosion-proof structure. When the battery heats up, the pressure reaches a certain degree of nicked fracture and deflation.

4. Various environmental abuse tests: conduct various abuse tests, such as external short circuit, overcharge, puncture, plate impact, incineration, etc., to inspect the safety performance of the battery. At the same time, the temperature impact test and the mechanical performance test of vibration, drop and impact were carried out to investigate the performance of the battery in the actual use environment.

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